1. Field of Invention
The present invention relates generally to a power supply for systems having an externally powered base unit and an associated rechargeable battery-powered portable unit. In particular, the present invention relates to an apparatus capable of charging two interchangeable rechargeable batteries simultaneously and further capable of utilizing one of those rechargeable batteries to power the base unit in the event of failure of the external power supply. While the present invention has utility in any system having an externally powered base unit and an associated rechargeable battery-powered portable unit, the invention has been disclosed in a cordless telephone embodiment. During the last decade the cordless telephone has dramatically invaded modern life such that the present invention has great utility when incorporated therein.
2. Background Art
Cordless telephones usually consist of one base unit and one handset. The base unit sends voice and data signals to its associated handset and receives voice and data signals from the handset over a radio frequency link. The data signals are utilized by the base unit to manipulate the subscriber telephone line, which is connected to the base unit. For instance, the base unit detects a ring signal on the telephone line and may further place the telephone line in an off-hook state if so directed by the user. The base unit further processes voice signals and transmits and receives both voice and data signals. Therefore the cordless telephone base unit, unlike a conventional line telephone, utilizes a great deal of power for which it must be connected to an external power source. Due to this external power connection, the cordless telephone will become inoperative during a power outage unlike its "corded" cousin, which may continue to receive power from the telephone company through the subscriber telephone line. Thus, in a household where the cordless telephone is the only telephone, the users would be without telephone service during a power outage.
The handset also manipulates voice and data and receives and transmits signals. Given its portability, the handset is usually powered by a rechargeable battery. These rechargeable batteries typically have a small voltage operating range in the cordless telephone handset and thus must be recharged often. Such recharging has typically been accomplished in prior devices by returning the handset with the rechargeable battery therein to the base unit cradle. Exposed charging terminals with the cradle mate with exposed contacts on the handset for charging the battery. However, as is often the case, the cordless telephone owner may forget to return the handset to the base unit for recharging and thus the telephone will ultimately become inoperable.
Accordingly, it is an object of the present invention to provide two interchangeable rechargeable batteries, such that when a user forgets to recharge the battery associated with the portable unit a second battery can be utilized to power the portable unit.
It is a further object of the present invention to provide an uninterruptable power supply for the base unit by utilizing the second rechargeable battery when it is charged and operably associated with the base unit to power the base unit circuitry in the event of a power failure.
These and other objects of the present invention will become apparent in light of the present specification, claims and drawings.